//
// detail/scheduler.hpp
// ~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2022 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#ifndef ASIO_DETAIL_SCHEDULER_HPP
#define ASIO_DETAIL_SCHEDULER_HPP

#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)

#include "asio/detail/config.hpp"

#include "asio/error_code.hpp"
#include "asio/execution_context.hpp"
#include "asio/detail/atomic_count.hpp"
#include "asio/detail/conditionally_enabled_event.hpp"
#include "asio/detail/conditionally_enabled_mutex.hpp"
#include "asio/detail/op_queue.hpp"
#include "asio/detail/scheduler_operation.hpp"
#include "asio/detail/scheduler_task.hpp"
#include "asio/detail/thread.hpp"
#include "asio/detail/thread_context.hpp"

#include "asio/detail/push_options.hpp"

namespace asio {
    namespace detail {

        struct scheduler_thread_info;

        class scheduler
                : public execution_context_service_base<scheduler>,
                  public thread_context {
        public:
            typedef scheduler_operation operation;

            // The type of a function used to obtain a task instance.
            typedef scheduler_task *(*get_task_func_type)(
                    asio::execution_context &);

            // Constructor. Specifies the number of concurrent threads that are likely to
            // run the scheduler. If set to 1 certain optimisation are performed.
            ASIO_DECL scheduler(asio::execution_context &ctx,
                                int concurrency_hint = 0, bool own_thread = true,
                                get_task_func_type get_task = &scheduler::get_default_task);

            // Destructor.
            ASIO_DECL ~scheduler();

            // Destroy all user-defined handler objects owned by the service.
            ASIO_DECL void shutdown();

            // Initialise the task, if required.
            ASIO_DECL void init_task();

            // Run the event loop until interrupted or no more work.
            ASIO_DECL std::size_t
            run(asio::error_code
            & ec);

            // Run until interrupted or one operation is performed.
            ASIO_DECL std::size_t
            run_one(asio::error_code
            & ec);

            // Run until timeout, interrupted, or one operation is performed.
            ASIO_DECL std::size_t

            wait_one(
                    long usec, asio::error_code &ec);

            // Poll for operations without blocking.
            ASIO_DECL std::size_t
            poll(asio::error_code
            & ec);

            // Poll for one operation without blocking.
            ASIO_DECL std::size_t
            poll_one(asio::error_code
            & ec);

            // Interrupt the event processing loop.
            ASIO_DECL void stop();

            // Determine whether the scheduler is stopped.
            ASIO_DECL bool stopped() const;

            // Restart in preparation for a subsequent run invocation.
            ASIO_DECL void restart();

            // Notify that some work has started.
            void work_started() {
                ++outstanding_work_;
            }

            // Used to compensate for a forthcoming work_finished call. Must be called
            // from within a scheduler-owned thread.
            ASIO_DECL void compensating_work_started();

            // Notify that some work has finished.
            void work_finished() {
                if (--outstanding_work_ == 0)
                    stop();
            }

            // Return whether a handler can be dispatched immediately.
            ASIO_DECL bool can_dispatch();

            /// Capture the current exception so it can be rethrown from a run function.
            ASIO_DECL void capture_current_exception();

            // Request invocation of the given operation and return immediately. Assumes
            // that work_started() has not yet been called for the operation.
            ASIO_DECL void post_immediate_completion(
                    operation *op, bool is_continuation);

            // Request invocation of the given operations and return immediately. Assumes
            // that work_started() has not yet been called for the operations.
            ASIO_DECL void post_immediate_completions(std::size_t n,
                                                      op_queue <operation> &ops, bool is_continuation);

            // Request invocation of the given operation and return immediately. Assumes
            // that work_started() was previously called for the operation.
            ASIO_DECL void post_deferred_completion(operation *op);

            // Request invocation of the given operations and return immediately. Assumes
            // that work_started() was previously called for each operation.
            ASIO_DECL void post_deferred_completions(op_queue <operation> &ops);

            // Enqueue the given operation following a failed attempt to dispatch the
            // operation for immediate invocation.
            ASIO_DECL void do_dispatch(operation *op);

            // Process unfinished operations as part of a shutdownoperation. Assumes that
            // work_started() was previously called for the operations.
            ASIO_DECL void abandon_operations(op_queue <operation> &ops);

            // Get the concurrency hint that was used to initialise the scheduler.
            int concurrency_hint() const {
                return concurrency_hint_;
            }

        private:
            // The mutex type used by this scheduler.
            typedef conditionally_enabled_mutex mutex;

            // The event type used by this scheduler.
            typedef conditionally_enabled_event event;

            // Structure containing thread-specific data.
            typedef scheduler_thread_info thread_info;

            // Run at most one operation. May block.
            ASIO_DECL std::size_t
            do_run_one(mutex::scoped_lock
            & lock,
            thread_info &this_thread,
            const asio::error_code &ec
            );

            // Run at most one operation with a timeout. May block.
            ASIO_DECL std::size_t
            do_wait_one(mutex::scoped_lock
            & lock,
            thread_info &this_thread,
            long usec,
            const asio::error_code &ec
            );

            // Poll for at most one operation.
            ASIO_DECL std::size_t
            do_poll_one(mutex::scoped_lock
            & lock,
            thread_info &this_thread,
            const asio::error_code &ec
            );

            // Stop the task and all idle threads.
            ASIO_DECL void stop_all_threads(mutex::scoped_lock &lock);

            // Wake a single idle thread, or the task, and always unlock the mutex.
            ASIO_DECL void wake_one_thread_and_unlock(
                    mutex::scoped_lock &lock);

            // Get the default task.
            ASIO_DECL static scheduler_task
            *
            get_default_task(
                    asio::execution_context
            & ctx);

            // Helper class to run the scheduler in its own thread.
            class thread_function;

            friend class thread_function;

            // Helper class to perform task-related operations on block exit.
            struct task_cleanup;
            friend struct task_cleanup;

            // Helper class to call work-related operations on block exit.
            struct work_cleanup;
            friend struct work_cleanup;

            // Whether to optimise for single-threaded use cases.
            const bool one_thread_;

            // Mutex to protect access to internal data.
            mutable mutex mutex_;

            // Event to wake up blocked threads.
            event wakeup_event_;

            // The task to be run by this service.
            scheduler_task *task_;

            // The function used to get the task.
            get_task_func_type get_task_;

            // Operation object to represent the position of the task in the queue.
            struct task_operation : operation {
                task_operation() : operation(0) {}
            } task_operation_;

            // Whether the task has been interrupted.
            bool task_interrupted_;

            // The count of unfinished work.
            atomic_count outstanding_work_;

            // The queue of handlers that are ready to be delivered.
            op_queue <operation> op_queue_;

            // Flag to indicate that the dispatcher has been stopped.
            bool stopped_;

            // Flag to indicate that the dispatcher has been shut down.
            bool shutdown_;

            // The concurrency hint used to initialise the scheduler.
            const int concurrency_hint_;

            // The thread that is running the scheduler.
            asio::detail::thread *thread_;
        };

    } // namespace detail
} // namespace asio

#include "asio/detail/pop_options.hpp"

#if defined(ASIO_HEADER_ONLY)
# include "asio/detail/impl/scheduler.ipp"
#endif // defined(ASIO_HEADER_ONLY)

#endif // ASIO_DETAIL_SCHEDULER_HPP
